How can I fake the date returned by java.time.LocalDate?

Question

I need to be able to fake the system time when testing. The source I have makes use of java.time.LocalDate. Is there a way to make LocalDate.now() return a pre-set date?

Answer 1

There are a few options you've:

1. Wrap the LocalDate.now() call in a non-static method of a class. Then you can mock that method to return your specific instance - This would not seem practical if you're directly calling LocalDate.now() method at many places in your code.

2. Use LocalDate.now(Clock) method, that is pretty test-friendly, as already suggested in comments - again you've to modify your application code.

3. Use Powermockito, if you can. In that case, you've a pretty easy approach by mocking static methods using mockStatic(Class<?>) method.

The 3rd approach can be implemented as:

@PrepareForTest({ LocalDate.class })
@RunWith(PowerMockRunner.class)
public class DateTest {
    @Test
    public void yourTest() {
        PowerMockito.mockStatic(LocalDate.class);
        when(LocalDate.now()).thenReturn(yourLocalDateObj);
    }
}

Answer 2

I would usually suggest using Mockito, but since the method is static, you can't really mock the object.

Why not have some "DateProvider" class grab the date for you

public class DateProvider{
   public LocalDate getNow(){
      return LocalDate.now();
   }
}

and use it thusly:

new DateProvider().getNow();

That would make it fairly easy to test with any LocalDate return value

Answer 3

Can you dependency inject the time through the constructor / parameter of the code?

Otherwise you can wrap LocalDate.now() in a static class that lets you hard-code a value for testing.

Answer 4

I was trying the code on this page but I noticed I should get the LocalDate instance first before to use PowerMockito as the 2 firstLines of the next code

@Test
public void testYearOptions() throws Exception{

    LocalDate date = LocalDate.of(2015,11,12);
    PowerMockito.mockStatic(LocalDate.class);

    Mockito.when(LocalDate.now()).thenReturn(date);
    Map<String, String> semesterMap = Utilities.getYears(); //Your function where LocalDate is Uses

    assertNotNull(yearsMap.get("2015"));//your assertion

}

Answer 5

No need of spaghetti code here: keep it simple! Write a convenience method and change its body to meet your needs.

public static LocalDate getCurrentTime() {
    // You can comment right code to save it during debugging
}

Answer 6

For testing:

@RunWith(SpringRunner.class)
@SpringBootTest
public class DateTimeFactoryTest {
  private static final Logger log = LoggerFactory.getLogger(DateTimeFactoryTest.class);

  @MockBean
  DateTimeFactory dateTimeFactory;

  @Test
  public void test001() throws MissingMethodInvocationException {
    given(dateTimeFactory.getLocalDate()).willReturn(LocalDate.of(2017,4, 4));
    LocalDate ld = dateTimeFactory.getLocalDate();
  }
}